Photoelectric tube



Nov. 24, 1942. A. N. ROGERS ETAL 2,303,174

v PHOTOELECTRICYTUBE Filed Jan. 25, 1941 .A ./v. ROGERS MEMO; 5.x. SHULL A T TOPNF V Patented Nov. 24, 1942 UNITED STATES T N T 'FFIQ E PHOTOELECTRIC TUBE Application January 25, 1941, Serial No. 375,892

4 Claims.

.This invention relates to space discharge devices and more particularly to photoelectric tubes.

An object of the invention is to provide an improved space discharge device.

A feature of the invention is a photoelectric tube of simple construction having several advantages over previously known more complicated structures.

In an example of practice illustrative of this invention a gas-tight container having a reentrant stem is provided with a semicylindrical hollow cathode and a coaxially positioned anode wire, both supported from said stem. A holder for a caesium producing mixture is mounted at the end of the container opposite from said stem in a position to direct caesium vapor toward the cathode as the mixture reacts chemically upon being inductively heated to the reaction temperature thereof. The caesium producing mixture is advantageously in the form of a compressed cylindrical pellet. During the sensitizing process the surface of the cathode, which is composed of pure "silver, is oxidized preparatory to having caesium deposited thereon. A mica disc is located between the upper end of the cathode and the pellet holder. This disc is spaced from the top of the cathode, being located closer to the cathode than to the pellet holder. The disc projects only a small distance beyond the front edges of the cathode thus forming a relatively large opening between the disc and the inside wall of the container.

The illustrative structure above described has several advantages over prior art structures ineluding simplicity and low cost of manufacture without sacrificing any of th advantages of more complicated prior art structures. The mounting of the pellet holder is exceedingly simple. Furthermore in the specific form described above the caesium vapor is emitted towards the inside walls of the container opposite the cathode which facilitates transfer of the caesium to the cathode surface. The mica disc serves both as a deflector plate for the hot caesium and as a filter to reduce the radiant heat reaching theoxidized cathode. Injuryof the oxide layer due to overheating is thus prevented. This construction, furthermore, permits of reducing the separation between the inductively heated pellet holder and the cathode. Still another function of the mica disc is to act as a stop or trap for material other than caesium vapor which may b ejected from the pellet holder during the reaction of the pellet. Another advantage of positioning the pellet holder so that the caesium is emitted toward the cathode, is that any such material other than the caesium which is ejected from the pellet holder deposits on the mica disc instead of on the inside of the container. Another important function of the mica disc is to prevent electrical discharge between the pellet holder and the concave surface of the cathode during the oxidation of the cathode by an electric discharge in oxygen thus enabling a more uniform roughening of the cathode and a more uniform layer of oxide to be obtained. Since the mica disc is in contact with the anode only, the leakage between the cathode and anode is a minimum.

From the foregoing it is clear that an improved photoelectric tube is provided by thi invention.

The invention will now be described more in detail having reference to the accompanying drawing:

Fig. 1 shows the structure of a completed photoelectric tube according to this invention;

Fig. 2 is a side view of the elements which are supported from the stem viewed from the lefthand side in Fig. 1; and

Fig. 3 is a front view of the elements shown in Fig. 2.

Like reference characters are used to refer to identical elements in the several figures.

The photoelectric tube illustrated in Fig. 1 comprises a glass bulb 5 having a reentrant stem 6 sealed therein. The stem 6 is provided with a press 1 in which are sealed support wires 8 and 9 for the cathode l0 and anode wire II. The cathode It) consists of a sheet of substantially pure silver of semicylindrical shape, the edges of which are formed around the support wires 8 and 9 and welded thereto. Supported from the free end of anode wire I l is a holder l2 for a caesium producing pellet which is used during the sensitizing process. This holder i2 comprises a nickel disc l3 to the under surface of which is secured a nickel gauze disc M by welding at a plurality of positions around the edges of the disc. An advantageous form of pellet comprises an intimate mixture of caesium chromate, chromic oxide and powdered aluminum compressed into a right cylinder, which on heating to the reaction temperature, produces caesium vapor by an exothermic reaction. The pellet is held tightly between the disc i3 and the gauze disc It. The immediate support for the holder I2 is the bent wire I5, one end of which is welded to the upper surface of the disc !3 and the other end to the anode wire Ii. Supported between the pellet holder I2 and cathode I0 is a mica disc It also secured to and supported by the wire l5 which passes through an eyelet in the mica disc. This eyelet is welded to the wire It. The mica disc [6 covers the top of the oathode IIJ and is separated from the cathode by a small space as shown. The front edge of the mica disc it extends only a little in front of the edges of the cathode l0. Sealed in the press I are lead-in wires i1 and I8 which are conrespect to the anode.

tainer 5 after the cathode has been oxidized,

The above described arrangementof the pellet described in greater detail in Patent No. 2,178,227

of M. S. Glass, patented October 31, 1939.

Other forms of holders for the caesium pellet may be used without sacrificing many of the advantages of this invention. Others of the alkali metals may be used, such as rubidium, lithium,

potassium, and sodium with suitable temperature variations. Other kinds and shapes of cathodes may be used. For example, the cathode may holder l2 and the mica disc I6 facilitates the I carrying out of the sensitizing process.

In this process occluded gases are first removed from the tube elements by heating in an oven without causing any chemical reaction in the caesium pellet. The concave surface of the cathode H! is prepared to receive the caesium vapor by oxidation and reduction to roughen the surface and by final oxidation leaving a layer of oxide of desired thickness thereon. The oxidation of the cathode surface is effected by an electric discharge between the cathode is and the anode wire H in an atmosphere of oxygen, the cathode being at a negative potential with It is at this point in the process that the mica disc l6 serves one of its functions, namely, that of facilitating the formation of a uniform laye of oxide by preventing a discharge between the holder l2 and the upper portions of the cathode it.

i2 is of metal and is conductively connected to the anode H, a discharge would take place between the holder l2 and the upper portions of the cathode It as well as between the anode wire H and the cathode E if the mica disc It were not present. The mica disc it prevents such discharge, the result being that a relatively uniform roughening and final oxidation of the concave surface of the cathode i8 is obtained. The mica disc 56 is placed close to the upper edge of the cathode iii to improve the uniformity of the discharge but is separated from the oathode it thereby making the leakage between the cathode and anode a minimum.

After the final layer of oxide has been formed caesium vapor is produced by inductive heating of the pellet holder I2. As the pellet reacts or flashes, hot caesium vapor is emitted and Since the holder another function of the mica disc l6 comes into play, namely, that of protecting the cathode from excessive heating which would reduce the oxide layer. The mica disc not only deflects the hot caesium vapor away from the oxidized cathode surface to the relatively cool walls of the container where it deposits, but it also acts as 'a filter to absorb much of the radiated heat rays. This disc also reflects heat rays. The mica of this disc is baked at a temperature of about 105 degrees centigrade for sixteen hours. One purpose of this baking is to free the mica of moisture. The mica disc also acts as a stop or trap for any hot material other than caesium vapor which might be ejected from the holder l2 during the reaction. The straight edge at the front of the mica disc it facilitates the emission of caesium vapor to the portion of the wall of the container in front of the cathode it and so aids 4 in the later transfer of the caesium to the concave cathode surface.

. The rest of the sensitizing process is then car ried out in a well-known manner including baking the container to drive the caesium to the concave surface of the cathode Ill, introducing such inert gases as desired, and sealing the container. An advantageous sensitizing pIOCBSS'IS comprise a nickel or copper sheet having a surface layer of silver which is processed in the manner hereinbefore described to render it photoemissive. A preliminary roughening of the silversurface may be accomplished in other ways than by oxidation and reduction of the silver oxide, as for example, by sand-blasting, etching with acid or even by applying a coating of silver oxide and a binder with a brush or air spray and reducing the silver oxide to metallic silver by heat.

What is claimed is:

l. A photoelectric tube comprising an envelope containing a light sensitive electrode including a curved plate provided with a coating of light sensitive material, another electrode spaced from a curved side of said curved plate and symmetrically disposed therewith, a conductive plate disposed at the end of said curved plate and supported from one of said electrodes, means having held reactive material employed in the coating of said curved plate with light sensitive material supported on said conductive plate, and a non-conductive disc located between said cathode and said conductive plate and spaced from both.

2. A photoelectric tube comprising an envelope containing a light sensitive electrode including a curved plate provided with a coating of light sensitive material, another electrode spaced from the hollow side of said curved plate and symmetrically disposed therewith, a conductive plate disposed at the end of said curved plate and supported on said other electrode, means having held reactive material employed in the coating of said curved plate with light sensitive material supported on said conductive plate, and a mica disc located between said cathode and said conductive plate and spaced from both.

3. A photoelectric tube comprising a container having a reentrant stem, a semicylindrical hollow silver cathode supported from said stem, an anode wire also supported from said stem coaxially with said cathode, a caesium pellet holder supported from said anode at the end away from said stem, said pellet holder comprising a metallic disc and an overlying gauze disc welded thereto on the side toward said cathode, and a mica disc at least as large as the topof said cathode also supportedfrom said anode between said pellet holder and said cathode.

4. A photoelectric tube comprising acontainer, a cathode mounted within said container and an anode also mounted within, said container in operative relation to said cathode, a caesium pellet holder also mounted within said container out of heat conducting contact with said cathode but supported on said anode, said pellet holder comprising a metallic disc and an overlying gauze disc welded thereto on the side toward said cathode, and a mica disc at least as large as the transverse section of said cathode also supported within said container between the said pellet holder and the said cathode.

ALFRED N. ROGERS. SHERMAN K, SHULL. 

